Add -rtc-td-hack option to fix time drift with RTC on Windows (Gleb Natapov)

After my last patch to fix interrupt coalescing was rejected
on the basis that it is too intrusive we decided to make the
fix much more localized and only fix the problem for RTC time
source. Unfortunately it is impossible to fix the problem entirely
inside RTC code like Andrzej proposed since Windows reads RTC
register C more then once on each time interrupt so it is impossible
to count reliably how many interrupt windows actually handled.
Proposed solution is localized to I386 target and is disabled by
default. To enable it "-rtc-td-hack" flag should be used.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6320 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 57 insertions, 0 deletions

diff --git a/hw/mc146818rtc.c b/hw/mc146818rtc.c
index f57a9a6783..cd57bf3760 100644
--- a/hw/mc146818rtc.c
+++ b/hw/mc146818rtc.c
@@ -67,6 +67,10 @@ struct RTCState {
     int64_t next_periodic_time;
     /* second update */
     int64_t next_second_time;
+#ifdef TARGET_I386
+    uint32_t irq_coalesced;
+    uint32_t period;
+#endif
     QEMUTimer *second_timer;
     QEMUTimer *second_timer2;
 };
@@ -104,12 +108,20 @@ static void rtc_timer_update(RTCState *s, int64_t current_time)
             period_code += 7;
         /* period in 32 Khz cycles */
         period = 1 << (period_code - 1);
+#ifdef TARGET_I386
+        if(period != s->period)
+            s->irq_coalesced = (s->irq_coalesced * s->period) / period;
+        s->period = period;
+#endif
         /* compute 32 khz clock */
         cur_clock = muldiv64(current_time, 32768, ticks_per_sec);
         next_irq_clock = (cur_clock & ~(period - 1)) + period;
         s->next_periodic_time = muldiv64(next_irq_clock, ticks_per_sec, 32768) + 1;
         qemu_mod_timer(s->periodic_timer, s->next_periodic_time);
     } else {
+#ifdef TARGET_I386
+        s->irq_coalesced = 0;
+#endif
         qemu_del_timer(s->periodic_timer);
     }
 }
@@ -119,6 +131,12 @@ static void rtc_periodic_timer(void *opaque)
     RTCState *s = opaque;
 
     rtc_timer_update(s, s->next_periodic_time);
+#ifdef TARGET_I386
+    if ((s->cmos_data[RTC_REG_C] & 0xc0) && rtc_td_hack) {
+        s->irq_coalesced++;
+        return;
+    }
+#endif
     s->cmos_data[RTC_REG_C] |= 0xc0;
     rtc_irq_raise(s->irq);
 }
@@ -379,6 +397,15 @@ static uint32_t cmos_ioport_read(void *opaque, uint32_t addr)
         case RTC_REG_C:
             ret = s->cmos_data[s->cmos_index];
             qemu_irq_lower(s->irq);
+#ifdef TARGET_I386
+            if(s->irq_coalesced) {
+                apic_reset_irq_delivered();
+                qemu_irq_raise(s->irq);
+                if (apic_get_irq_delivered())
+                    s->irq_coalesced--;
+                break;
+            }
+#endif
             s->cmos_data[RTC_REG_C] = 0x00;
             break;
         default:
@@ -473,6 +500,28 @@ static int rtc_load(QEMUFile *f, void *opaque, int version_id)
     return 0;
 }
 
+#ifdef TARGET_I386
+static void rtc_save_td(QEMUFile *f, void *opaque)
+{
+    RTCState *s = opaque;
+
+    qemu_put_be32(f, s->irq_coalesced);
+    qemu_put_be32(f, s->period);
+}
+
+static int rtc_load_td(QEMUFile *f, void *opaque, int version_id)
+{
+    RTCState *s = opaque;
+
+    if (version_id != 1)
+        return -EINVAL;
+
+    s->irq_coalesced = qemu_get_be32(f);
+    s->period = qemu_get_be32(f);
+    return 0;
+}
+#endif
+
 RTCState *rtc_init(int base, qemu_irq irq)
 {
     RTCState *s;
@@ -503,6 +552,10 @@ RTCState *rtc_init(int base, qemu_irq irq)
     register_ioport_read(base, 2, 1, cmos_ioport_read, s);
 
     register_savevm("mc146818rtc", base, 1, rtc_save, rtc_load, s);
+#ifdef TARGET_I386
+    if (rtc_td_hack)
+        register_savevm("mc146818rtc-td", base, 1, rtc_save_td, rtc_load_td, s);
+#endif
     return s;
 }
 
@@ -609,5 +662,9 @@ RTCState *rtc_mm_init(target_phys_addr_t base, int it_shift, qemu_irq irq)
     cpu_register_physical_memory(base, 2 << it_shift, io_memory);
 
     register_savevm("mc146818rtc", base, 1, rtc_save, rtc_load, s);
+#ifdef TARGET_I386
+    if (rtc_td_hack)
+        register_savevm("mc146818rtc-td", base, 1, rtc_save_td, rtc_load_td, s);
+#endif
     return s;
 }